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Welcome back. One of my staple YouTube Subscriptions. I’m today years old learning that the light that we actually see on earth today came out 100s of thousand

Welcome back. One of my staple YouTube Subscriptions. I’m today years old learning that the light that we actually see on earth today came out 100s of thousands of years ago.

PunchyHamster 8mo ago
[flagged]
- JeanSebTr 8mo ago
  They probably meant, as explained in the video, "light from our sun"
- MyHonestOpinon 8mo ago
  Oh, probably skipped physics too. I haven't seen the video (yet), but I would have bet that light on earth came out 8 minutes ago from the sun.
  - pantulis 8mo ago
    Light from the sun that is reaching us now escaped the surface of the sun 8 minutes ago, yes. But photons are generated in the core through nuclear reactions, where they take their sweet amount of thousands of years bouncing around until they get out.
    - gpvos 8mo ago
      And thats a fact you don't need to learn in high school, at least you didn't in my time.
    - mikkupikku 8mo ago
      I think this is right in a certain sense, but not precisely. From what I understand no visible light photons are created in the core from nuclear fusion, it's mostly a bunch of gamma rays that get almost immediately absorbed. The energy, but not the photons from fusion, gets transfered up through the layers of the sun, through radiation and convection, eventually heating the photosphere. It is then the photosphere, white hot, which ultimately radiates the visible light we see as sunlight.
      - pantulis 8mo ago
        Thanks for your answer, I understand you're correct. Also, as another counterargument, if a photon is scattered... is it the same photon or a different one? Your perspective on energy instead of particles is better.
- smarf 8mo ago
  ...did you skip human socialization?
gosub100 8mo ago
It's not the same photon though. The fusion happens in the core, then takes millennia for the energy to escape. During that time photons are emitted and absorbed by the atoms, until the surface emits one that finally travels to the earth in 8 minutes. Anyway that's taking you from the ELI5 to the ELI9 version. I'm sure someone on here can correct it further.
- amluto 8mo ago
  I haven’t tried to look up the history of this claim, but here are some guesses: 1. There’s a sort of diffusion process going on. Photons from the core have some mean free path as a function of radial position (and, obnoxiously, of wavelength as well, so maybe we ignore that). You could calculate the mean time for a hypothetical object emitted from the core and traveling according to those mean free paths to escape. 2. You could imagine you have marked a photon and watched it travel. This is quite problematic. First, photons in thermal equilibrium obey Bose-Einstein statistics because they are indistinguishable bosons, and anything that could mark them would change the statistics to that of distinguishable particles. But whatever, the temperature is high and maybe this doesn’t matter. Also never mind that those core photons are mostly much shorter wavelength than the photons we see. But you can still imagine. (The answer is probably quite similar to #1 since this is sort of the same problem depending on how you think about the interactions with matter in the sun.) 3. You could calculate how long it would take to notice anything if the core suddenly stopped fusing.
  - gus_massa 8mo ago
    I agree. I read the 5000 years time a few times and I don't like it. When you have a transparent medium like water or glass, the photon that enters and the photon that exit share a lot of properties, in particular energy/color/frequency. Perhaps they have a shift in the phase or a different polarization (like in water with sugar or if you want to be fancy a quarter wave plate). You can still split a beam before in enter and make interference experiments after half of it passed though water or glass, and other weird experiments, so I think it's fair to call them "the same photon". But in the Sun, the original photons in the center of the Sun have a few very specific values of energy/color/frequency, that are totally lost. (But the neutrinos have so few interactions that they don't lose this information, and it's possible to do neutrino spectroscopy!) Also, the photons emitted by the "surface" of the Sun have a wide spectrum of energy/color/frequency that is very close to black body radiation at something like 5000K-6000K. So in my opinion it's better to think that the original photon in the center is absorbed shortly after it's emitted, and transformed into heat. The heat takes 5000 years to get to the surface. And then the hot surface emits a few new photons unrelated to the original one. I'm not sure what is the main transmission method inside the Sun: conduction, convection or radiation.

Welcome back. One of my staple YouTube Subscriptions. I’m today years old learning that the light that we actually see on earth today came out 100s of thousands of years ago.

PunchyHamster 8mo ago

[flagged]

JeanSebTr 8mo ago
They probably meant, as explained in the video, "light from our sun"
MyHonestOpinon 8mo ago
Oh, probably skipped physics too. I haven't seen the video (yet), but I would have bet that light on earth came out 8 minutes ago from the sun.
- pantulis 8mo ago
  Light from the sun that is reaching us now escaped the surface of the sun 8 minutes ago, yes. But photons are generated in the core through nuclear reactions, where they take their sweet amount of thousands of years bouncing around until they get out.
  - gpvos 8mo ago
    And thats a fact you don't need to learn in high school, at least you didn't in my time.
  - mikkupikku 8mo ago
    I think this is right in a certain sense, but not precisely. From what I understand no visible light photons are created in the core from nuclear fusion, it's mostly a bunch of gamma rays that get almost immediately absorbed. The energy, but not the photons from fusion, gets transfered up through the layers of the sun, through radiation and convection, eventually heating the photosphere. It is then the photosphere, white hot, which ultimately radiates the visible light we see as sunlight.
    - pantulis 8mo ago
      Thanks for your answer, I understand you're correct. Also, as another counterargument, if a photon is scattered... is it the same photon or a different one? Your perspective on energy instead of particles is better.
smarf 8mo ago
...did you skip human socialization?

gosub100 8mo ago

It's not the same photon though. The fusion happens in the core, then takes millennia for the energy to escape. During that time photons are emitted and absorbed by the atoms, until the surface emits one that finally travels to the earth in 8 minutes. Anyway that's taking you from the ELI5 to the ELI9 version. I'm sure someone on here can correct it further.

amluto 8mo ago
I haven’t tried to look up the history of this claim, but here are some guesses: 1. There’s a sort of diffusion process going on. Photons from the core have some mean free path as a function of radial position (and, obnoxiously, of wavelength as well, so maybe we ignore that). You could calculate the mean time for a hypothetical object emitted from the core and traveling according to those mean free paths to escape. 2. You could imagine you have marked a photon and watched it travel. This is quite problematic. First, photons in thermal equilibrium obey Bose-Einstein statistics because they are indistinguishable bosons, and anything that could mark them would change the statistics to that of distinguishable particles. But whatever, the temperature is high and maybe this doesn’t matter. Also never mind that those core photons are mostly much shorter wavelength than the photons we see. But you can still imagine. (The answer is probably quite similar to #1 since this is sort of the same problem depending on how you think about the interactions with matter in the sun.) 3. You could calculate how long it would take to notice anything if the core suddenly stopped fusing.
- gus_massa 8mo ago
  I agree. I read the 5000 years time a few times and I don't like it. When you have a transparent medium like water or glass, the photon that enters and the photon that exit share a lot of properties, in particular energy/color/frequency. Perhaps they have a shift in the phase or a different polarization (like in water with sugar or if you want to be fancy a quarter wave plate). You can still split a beam before in enter and make interference experiments after half of it passed though water or glass, and other weird experiments, so I think it's fair to call them "the same photon". But in the Sun, the original photons in the center of the Sun have a few very specific values of energy/color/frequency, that are totally lost. (But the neutrinos have so few interactions that they don't lose this information, and it's possible to do neutrino spectroscopy!) Also, the photons emitted by the "surface" of the Sun have a wide spectrum of energy/color/frequency that is very close to black body radiation at something like 5000K-6000K. So in my opinion it's better to think that the original photon in the center is absorbed shortly after it's emitted, and transformed into heat. The heat takes 5000 years to get to the surface. And then the hot surface emits a few new photons unrelated to the original one. I'm not sure what is the main transmission method inside the Sun: conduction, convection or radiation.